What is pneumonia?

Pneumonia is a type of chest infection.

It affects the tiny air sacs in your lungs, called alveoli. When you have pneumonia, these air sacs get inflamed and fill with fluid. This makes it harder for you to breathe.

Diagram of the lungs, airways, bronchioles, and air sacs

Most people with pneumonia can be completely cured. But it can be life-threatening, and you should take it seriously even if you’re young and fit.

Next: Who's at risk of pneumonia? >


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Last medically reviewed: October 2016. Due for review: October 2019

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.